As shown in cited Japanese Laid Open Patent Publication Nos. JP(A) H6-307535 and JP(A) H11-159608, for a vehicle loaded with an automatic transmission equipped with a torque converter having lockup features, fuel consumption improvement is attempted by locking up the converter under different conditions, such as driving at a predetermined speed or more and other accelerator statuses.
Moreover, in cited Japanese Laid Open Patent Publication No. JP(A) 2001-330127, a vehicle is equipped with a continuously variable transmission as the automatic transmission.
However, prolongation of the fuel-cut time is normally attempted when a vehicle is coasting by achieving a lockup state, thus sustaining a constant engine rpm and making the lockup-canceling vehicle speed as low as possible.
When this lockup occurs during the coasting period, it makes the driver feel as though the engine brake has been applied, but this engine brake feeling is less objectionable for the driver when the driver has intentionally stepped on the brake pedal when the brake is ON than when the brake is OFF.
Therefore, the lockup-canceling vehicle speed can be set to the lower vehicle speed side when the brake is ON compared to when the brake is OFF.
However, when the driver changes the leg position from the accelerator pedal to the brake pedal (accelerator OFF and brake ON) while the vehicle is moving at a steady state or accelerating with the automatic transmission locked up at a vehicle speed that is higher than the lockup-canceling vehicle speed for the brake ON status but lower than the lockup-canceling vehicle speed for the brake OFF status, the status goes through the accelerator OFF status and the brake OFF status while the driver is changing the leg position, causing the lockup to be cancelled.
Therefore, this causes a problem in that the fuel-cut time is shortened and the fuel consumption rate deteriorates.
It also causes other problems in that shortening of the fuel-cut time cannot be avoided even if the lockup state is restored by detecting the brake ON status after the lockup is cancelled due to the delay that occurs between the two states, resulting in poorer drivability of the vehicle due to the fluctuation of the engine rpm that occurs when returning to the lockup state.
Furthermore, it causes similar problems associated with fuel consumption and drivability when the driver changes the leg position from the brake pedal to the accelerator pedal (brake OFF and accelerator ON) while the vehicle is decelerating with the brake turned ON at a vehicle speed that is higher than the lockup-canceling vehicle speed for the brake ON status but lower than the lockup-canceling vehicle speed for the brake OFF status, because the lockup state gets cancelled while the driver is changing the leg position.